COFACTORS OF EnzYMIC ADAPTATION 229 



stimulation brought about by cofactor E which is very much 

 greater and relatively constant. 



Only few experiments were done on the mechanism of 

 action of E. It can be metabolized by the cells into an inactive 

 form. This can be demonstrated by adding first the cofactor 

 and delaying the addition of maltose. The stimulation is much 

 smaller than the one produced by simultaneous addition of 

 both compounds. Furthermore, the same experiment clearly 

 shows that the cofactor acts in a different way from the 

 inducer and does not replace it. 



Spontaneous "petite" mutation 



Ephrussi and Leupold (unpublished) discovered certain 

 yeast strains that present a much higher spontaneous mutabil- 

 ity than usual. Preliminary experiments were carried out 

 with one of these (strain C982/19b). The results were rather 

 unexpected. Adenine and cofactor E seem to increase the 

 percentage of mutants, while cofactor T seems to decrease it. 

 It is interesting to note that, although the roles are reversed, 

 the coupling of cofactor E with adenine is maintained. 

 However, a possible effect on the selection rather than on the 

 mutation frequency has yet not been excluded. 



Acknowledgement 



The authors gratefully acknowledge the continued interest of Prof. 

 B. Ephrussi and the advice and help of Prof. E. Lederer and Dr. J. 

 Asselineau. Our thanks are due to Prof. Frerejacque, Drs. B. L. 

 Horecker, A. S. Perlin, N. K. Richtmyer and F. Skoog, who kindly put 

 at our disposal samples of rare sugars or their derivatives. 



REFERENCES 



Ephrussi B. (1953). Nucleocytoplasmic Relations in Micro-organ- 

 isms. Oxford University Press. 



Ephrussi, B., and Slonimski, P. (1950). Biochim. hiophys. acta, 6, 256. 



Ephrussi B., Slonimski, P., and Yotsuyanagi, Y. (1955). Nature, 

 LoncL, 176, 1207. 



Ephrussi, B., Slonimski, P., Yotsuyanagi, Y., and Tavlitzki, J. 

 (1956). C. R. Lab. Carlsberg, Ser. physioL, 26, 87. 



Gale, E. F. (1951). Chemical Activities of Bacteria. Cambridge 

 University Press. 



